I have read a few books of osho including love's mystery .and liked them all.
Please tell me ,for a person who has lost track of his beloved very soon after falling in love with her.and is lovesick in her separation,what english books of osho particularly speak about this kind of painfull separation .I want to know the psychology of it .and how it can be transformed into steps towards inlightenment
Please list the books in order of relrevance to the mater
Thank you in advance..

I don't think Osho has spoken partilcarly on Love only in any Book. May be you can get some compiled book of Osho on Love Only.

Two links which will be very helpful to you are

Osho on love, relationships and Personality

Osho on Death and Dying

And Osho Teachings Blog

I hope it has helped you
Meditate and Meditate

Sorry
Right link for Osho on Death and Dying